1. Field of the Invention
The present invention relates to a control apparatus and method. More particularly, the present invention relates to a light source control apparatus and a method for controlling a light source.
2. Description of Related Art
RGB light emitting diodes (LEDs) can exhibit a wider color gamut as compared with cold cathode fluorescent lamps (CCFLs), wherein R, G, B are red, green, and blue signals of three primary colors. Therefore, LED has a more diversified color performance than the CCFL, and has been widely used as light-emitting sources of liquid crystal displays (LCD).
However, since the size of the LCDs is increasingly enlarged, and the number of the LEDs used in an LCD of a larger size usually reaches several hundreds. Therefore, the LEDs in the LCD are usually connected in series or in parallel, so as to reduce the number of parts for controlling the LEDs. However, this control method may degrade the quality of images, as shown in FIG. 1.
FIG. 1 shows a conventional LED control apparatus disposed in the LCD. The LED control apparatus is used to control the light-emitting brightness of the LEDs 101-10N, and the LEDs 101-10N are a string of LEDs connected in series in the LCD. The control apparatus in the figure includes a brightness measuring circuit 100-1 having a photosensitive diode 100-2, an analog-digital converter 100-3, a control circuit 100-4, a power metal-oxide-semiconductor (MOS) transistor 100-5, and a resistor 100-6. Moreover, a source voltage and a common level are respectively indicated by VCC and COM.
The conventional control device uses a resistor 100-6 to obtain a feedback signal FB, so as to make the feedback signal FB tracking a reference voltage VFB in the control circuit 100-4 to generate a pulse width modulation signal PWM to control the tuning on of the power MOS transistor 100-5, so that the current passing through the resistor 100-6 is I=VFB/resistor 100-6. According to Kirchhoff's current law (KCL), the current will also pass through the LEDs 101-10N. The spectrum emitted by the LEDs are measured through the brightness measuring circuit 100-1, and converted into a digital signal by using the analog-digital converter 100-3, and then transmitted to the control circuit 100-4, so that the control circuit 100-4 can adjust the LEDs to the desired spectrum range according to the pulse width modulation signal PWM.
However, the temperature coefficients and degrees of aging of the LEDs are not completely identical, so that the light-emitting situation of each LED varies, and the circuit architecture of the conventional control apparatus can not adjust the LED individually, thus degrading the image quality of LCDs.
Moreover, as the conventional architecture can only amend the brightness of the LEDs 101-10N at the same time, and the brightness compensation can not be performed on an individual LED, the image quality is degraded. Therefore, a strict quality control is necessary for mass production, and the manufacturing cost remains high, and the quality is still difficult to control.